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This diagram has a heading “Doing.” Underneath, the word “number’ is written, followed by an arrow pointing to a box. The box contains the operation “add 5.” From the box, a further arrow points to a second box which contains the operation “multiply by 3.” From the second box, a further arrow points to a third box which contains the operation “subtract 4.” From this box, an arrow points to the answer 17. Under the first diagram there is a heading “Undoing.” The number 17 is followed by an arrow which points to a box. The box contains the operation “add 4.” The output from this operation is 17 + 4 =21 and a further arrow with the answer 21 above it points to a second box. This box contains the operation “divide by 3.” The output from this operation is 21 divided by 3 = 7 and a further arrow with the answer 7 above it points to a third box. This box contains the operation “subtract 5” and a further arrow points to the answer 2 (since 7 – 5 = 2).

 9.5.2 Doing and Undoing